The present invention relates to a composite material with an improved structure having dispersed therein an active organic compound, as well as to an effluent treatment process, especially a photographic effluent treatment process.
Many manufacturing and processing steps are carried out in an aqueous phase, thereby generating aqueous effluents. One example of this is the photographic industry, in which exposed silver halide photographic films and papers pass through several aqueous processing baths. A photographic treatment generally comprises several processing baths and one or more wash and (or) stabilization baths.
These processes entail a high consumption of water. Owing to new stricter environmental legislation, new standards forbid the discarding of wastewater directly into the sewers without prior treatment, and in particular require a reduction in the consumption of water for photographic processing. The problem is that reducing the volume of water allowed favors bacterial pollution. The growth of microorganisms in aqueous solutions and in particular in prebaths, stabilization baths and wash baths is well known, and worsens as soon as the quantity of water consumed is reduced. The growth of microorganisms, if not controlled, causes the formation of sludge that clog equipment, adversely affect the process bath and so impair the quality of the resulting photographic image. In the field of traditional medical imaging, for example, it is desirable to reduce bacterial proliferation as much as possible because the bacteria cause defects on developed films. Such defects can lead to errors of diagnosis. In addition, bacterial proliferation causes the formation of a biofilm on the walls of the processing tanks and on the rollers and film drive sprockets, so that machinery has to be shut down for cleaning.
Bacterial growth control agents are commonly used to prevent or limit biological growth in processing solutions. For greater security, quantities in excess of those theoretically required are used. The result is that the wastewater discharged into the environment contains large quantities of bacterial growth control agents, which cause problems in sewage treatment centers that use the action of microorganisms to treat waste water.
Publication EP-A-937 393 describes a composite material and a method for preparing it, which comprises hydrolysing in a basic medium an alkylalkoxysilane of the formula RSiR1x(OR2)3xe2x88x92x wherein R is an alkyl group comprising a SH or xe2x80x94S(xe2x80x94CH2)nxe2x80x94Sxe2x80x94 function wherein n is from 0 to 4, R1 and R2 are independently a methyl or ethyl group, x is 0 or 1, in the presence of an active organic compound and an aqueous solution of an inorganic imogolite gel in fiber form comprising active hydroxyl groups on the fiber surface.
The composite material obtained by this method comprises an organic-inorganic polymer matrix that is an imogolite gel in fiber form on which are grafted sulfur-containing molecules to capture the silver present in the wash water. In the matrix is dispersed an active organic compound such as a bacterial growth control agent. The composite material takes the form of a gel in which the active organic compound is trapped. When it is placed in contact with an aqueous effluent, the trapped active organic compound is slowly released into the effluent. In this material the imogolite fibers are interconnected by chemical hydrogen bonds, giving a physical gel. However, this physical gel is not dense enough to retain in its matrix the hydrophilic active organic compounds, which thus tend to diffuse too rapidly into the effluent. It is then no longer possible to control the quantity of active organic compound diffusing into the effluent. In addition, because the physical gel is thixotropic, it is relatively mobile when it is being handled, and so is difficult to package for subsequent commercialization.
The present invention provides a new material that allows a set quantity of active organic compound to be gradually released into an effluent, in particular when this active organic compound is hydrophilic.
The present invention provides also a material that is easy to package.
The present invention relates to a composite material that takes the form of a structured gel, comprising an aluminosilicate polymer matrix in the form of an imogolite gel made up of fibers, in which at least two distinct fibers are interconnected by at least two covalent bonds to form an irreversible chemical gel, and having dispersed therein an active organic compound. Owing to said covalent bonds, the material of the invention takes the form of a structured gel, and so retains the active organic compounds more effectively, especially hydrophilic compounds trapped in the matrix, thereby better controlling their diffusion out of the matrix. It is also more compact and can be packaged more easily for marketing.
The present invention further concerns a method of obtaining such a composite material. This process comprises the hydrolysis in basic medium of at least one structuring agent in the presence of an active organic compound and an aqueous solution of an inorganic imogolite gel made up of fibers comprising active hydroxyl groups on the surface, said structuring agent containing at least two leaving groups reacting with said active hydroxyl groups to form at least two covalent bonds between at least two distinct imogolite fibers to yield an irreversible chemical gel.
The term xe2x80x9cactive hydroxyl groupsxe2x80x9d here means groups able to react with the structuring agent in an aqueous medium.
The invention also relates to a method of treating a medium with said active organic compound, as well as a device for carrying out said method. This treatment method comprises contacting the composite material of the invention with said medium. The method of the invention is especially efficient for the treatment of photographic baths, in particular for releasing a set quantity of bacterial growth control agent into said baths, and especially when said control agent is hydrophilic.